1. Field of the Invention
The present invention relates to Pitot Array Flow Elements wherein the tubes are of a different material than the housing or shell of the flow element. In such an arrangement, the present invention provides for the differential expansion between the tube expansion and the shell or housing expansion. Further, the present invention provides for the movement of the tubes within the packing assembly without penetrating the shell or housing of the flow element.
2. Description of the Related Art
The Pitot tube operates based upon the principal that when a fixed probe is inserted into piping or duct work containing a moving fluid, the total pressure sensed by the probe is the sum of the static pressure exerted by the fluid, whether in motion or at rest, and the dynamic pressure equivalent to the kinetic energy of the fluid in motion. Conventional Pitot tube arrangements provide measurement of both the static and total pressure of the flowing fluid, the difference between which is the dynamic pressure. This differential pressure, i.e. the dynamic pressure, is directly related to and can be used to calculate the linear flow rate within the piping or duct work. The volumetric flow rate of the fluid is determined by multiplying the linear flow rate by the cross-sectional area of the conduit.
Recent advances in the development of high temperature gas flow sensing elements are known. Particularly, in U.S. Pat. No. 5,736,651, issued to the present applicant, and incorporated herein by reference as if fully rewritten, a high temperature gas flow sensing element was first described using a ribbon packing or packing ring comprised of GRAPHOIL™ packing material, as manufactured by U-CAR™, or similar and equivalent material. Such a packing remains pliable to seal around Pitot tubes while still permitting lateral motion of the Pitot tubes which is encountered when thermal differential expansion occurs. Such an innovation solves the particular problem of leakage between the sensing tube ends where they are connected at the sensing element head and the duct sidewall that these tubes must penetrate.
However, such a solution is applicable only where the traverse tubes of the flow element penetrate the shell, but is not achievable in situations where connections outside the flow element are not possible due to physical constraints (such as where two or more air flow ducts are physically butted against each other). Up until now, no acceptable solution has existed in such applications.
Consequently, a need exists to provide an improved assembly for air flow elements used with high temperature flow elements where the tubes are allowed to expand and contract independent of the flow element shell when no shell penetration of the tubes can exist.